Chandan D Sharma, 497489 Rainbow Dr, Cupertino, CA 95014

6678422, Jan 13, 2004

Aug 30, 2000

09/651991

Chandan Dev Sharma - Sunnyvale CA
Bernd Meyer - Santa Clara CA

National Semiconductor Corporation - Santa Clara CA

G06K 936

382240

A method and apparatus for performing a multi-stage wavelet transform on a block of image data, using a smaller memory than would be required to implement an equivalent conventional multi-stage wavelet transform on the same block, and a method and apparatus for performing compression on a block of image data by performing a multi-stage wavelet transform on the block, quantizing coefficients resulting from the multi-stage wavelet transform, and performing entropy encoding on the quantized coefficients. Typically, the input image data is generated by a document scanner, and is compressed in a manner allowing fast decompression (by employing simple entropy encoding) and imposing low memory requirements. The data is compressed by operating a first circuit to perform at least two consecutive horizontal wavelet transform stages on a block of the image data, quantizing and entropy encoding at least a first block of the resulting coefficients indicative of relatively high spatial frequency information (âhigh frequency coefficientsâ) and writing to a memory a second block of the resulting coefficients indicative of relatively low spatial frequency information (âlow frequency coefficientsâ), reading the low frequency coefficients from memory and operating a second circuit to perform at least one vertical wavelet transform stage on the low frequency coefficients, and quantizing and entropy encoding at least some of the resulting coefficients.